function plus(){
    var number=document.getElementById("number");
    number.value++;
    document.getElementById("number").innerHTML=number.value;
}
function subtract(){
    var number=document.getElementById("number");
    number.value--;
    document.getElementById("number").innerHTML=number.value;
}
function sum(){
    var price=document.getElementById("price");
    var number=document.getElementById("number");
    money.value=price.value*number.value;
}